Hello,
I'm using ptp4l on a device with 2 ethernet interfaces with ptp support.
We configure one interface to use for synchronzation with udpv4 as
transport protocol which works fine.
Lately I found that if configuring both interfaces to be in the same
IPv4 subnet, synchronization stopped working even if forcing the
interface to use.
I looked through the the code (udp.c) and found the function
mcast_bind() that should force the interface for sending. It uses the
socket option IP_MULTICAST_IF with a structure carrying the interface index.
The same socket option may also be called with the ipv4 address of the
interface. I tried this variant and it works fine.
Attached you can find a patch with my changes.
kind regards,
Matthias
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From d6668b69432fba5916b63965332d5206619939c9 Mon Sep 17 00:00:00 2001
From: Matthias Loy <matthias....@hbm.com>
Date: Wed, 27 Sep 2017 13:23:14 +0200
Subject: [PATCH] make sure to send udpv4 over specific interface
---
udp.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/udp.c b/udp.c
index 6dabc31..737fb24 100644
--- a/udp.c
+++ b/udp.c
@@ -20,7 +20,6 @@
#include <errno.h>
#include <fcntl.h>
#include <net/if.h>
-#include <netdb.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
@@ -49,6 +48,8 @@ struct udp {
struct address mac;
};
+static int udp_protocol_addr(struct transport *t, uint8_t *addr);
+
static int mcast_bind(int fd, int index)
{
int err;
@@ -243,6 +244,16 @@ static int udp_send(struct transport *t, struct fdarray *fda, int event,
if (event == TRANS_ONESTEP)
len += 2;
+ struct in_addr ifAddr;
+
+ udp_protocol_addr(t, &ifAddr);
+
+ /* make sure to send over this interface */
+ if (setsockopt(fd, IPPROTO_IP, IP_MULTICAST_IF, &ifAddr, sizeof(ifAddr))) {
+ pr_err("Error setsockopt IP_MULTICAST_IF for interface");
+ return -1;
+ }
+
cnt = sendto(fd, buf, len, 0, &addr->sa, sizeof(addr->sin));
if (cnt < 1) {
pr_err("sendto failed: %m");
--
2.7.4
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